The present invention relates to a solid state image-pickup device, and particularly to a solid state image-pickup device of the MOS-type and a solid state image-pickup device of the charge-storage-type. More particularly, the invention relates to a solid state image-pickup device in which a dynamic range is expanded so that light reception from a subject having a high luminous intensity can be made without saturation.
Conventionally, a solid state image-pickup device of the MOS-type as shown in FIG. 1 has been employed. As seen in the drawing, the solid state image-pickup device is arranged in a manner so that a plurality of photodiodes PD.sub.11 .about.PD.sub.nm are arranged in the form of a matrix. A plurality of vertically extending signal reading lines L.sub.1 .about.L.sub.m and horizontally extending control-signal lines C.sub.1 .about.C.sub.n are distributed so as to cross each other at positions of the respective photodiodes. Further, MOS switching elements M.sub.11 .about.M.sub.nm are provided to transfer signal charges of the respective photodiodes to predetermined ones of the signal-reading lines when they are made conductive by scanning signals from predetermined ones of the control-signal lines. The signal-reading lines L.sub.1 .about.L.sub.m are connected at their terminals to a common output signal line Q through corresponding MOS switching elements G.sub.1 .about.G.sub.m, respectively. The on-off operation of the switching elements G.sub.1 .about.G.sub.m is controlled by corresponding horizontal scanning signals H.sub.1 .about..sub.Hm, respectively, supplied from the respective output terminals of a horizontal shift register 1. On the other hand, the terminals of the control signal lines C.sub.1 .about.C.sub.n are connected to the respective output terminals of a vertical shift register 2 and are supplied with vertical scanning signals V.sub.1 .about.V.sub.n, respectively.
Referring to FIGS. 1 and 2, the operation of the solid state image-pickup device of the MOS-type will be described hereunder. First, a start signal CKV is supplied to the vertical shift register 2 (at a point of time t.sub.1 in FIG. 2), and the signal CKV is succeedingly transferred in synchronism with synchronizing signals .phi..sub.H1 and .phi..sub.H2 each having a predetermined period so as to generate m pulses of horizontal scanning signals H.sub.1 .about.H.sub.m in each period of .tau..
The switching elements M.sub.11 .about.M.sub.nm and G.sub.1 .about.G.sub.m are controlled so as to be conductive/non-conductive at a predetermined timing in synchronism with the scanning signals V.sub.1 .about.V.sub.n and H.sub.1 .about.H.sub.m, so that the signal charges generated in the respective photodiodes are outputted as a time series signal to an output terminal 3 through so-called horizontal and vertical scanning.
In such a conventional MOS solid state image-pickup device, however, there has been a problem in that in the case of taking a photograph of a subject having a high luminous intensity, the photodiodes are saturated so that a so-called dynamic range can not be sufficiently expanded.
Conventionally, on the other hand, a solid state image-pickup device of the charge-storage-type having such an arrangement as shown in FIG. 3 has been employed. Referring to FIG. 3, first, the arrangement will be described. The image-pickup device is of a so-called inter-line transfer system in which a plurality of photodiodes P.sub.11 '.about.P.sub.mn ' are arranged in the form of a matrix among a plurality of vertical transfer lines L.sub.1 '.about.L.sub.n '. A horizontal transfer line H' is connected to the vertical transfer lines P.sub.11 '.about.P.sub.mn ' at their terminals, and the terminal of the horizontal transfer line H' is connected to an output terminal Q' through an impedance conversion amplifier AMP'.
The operation will be described hereunder. First, the solid state image-pickup device is exposed to light for a predetermined time so as to generate signal charges in selected ones of the photodiodes P.sub.11 '.about.P.sub.mn ', and the signal charges are transferred from the photodiodes P.sub.11 '.about.P.sub.mn ' to corresponding ones of the vertical transfer lines L.sub.1 '.about.L.sub.n ' opposite to the selected ones of the photodiodes P.sub.11 '.about.P.sub.mn ' through transfer gates (not shown), respectively. Thus, the signal charges are transferred to predetermined pixels in the vertical transfer lines so as to be made transferable.
Next, driving signals of a so-called four-phase driving system or the like are applied to transfer electrodes (not shown) of the vertical transfer lines L.sub.1 '.about.L.sub.n ', so that a row of signal charges generated in the horizontally arranged ones of the photodiodes are transferred to the horizontal transfer line H', and simultaneously all the signal charges are similarly shifted vertically. Succeedingly, the row of the signal charges on the horizontal transfer line H' are serially outputted from the horizontal transfer line H' to the output terminal Q' through the impedance conversion amplifier AMP'. The above operation in which one row of the horizontally aligned signal charges in the vertical transfer lines L.sub.1 '.about.L.sub.n ' are outputted through the horizontal transfer line H' is repeated with respect to the whole of the signal charges, so that all of the signal charges can be outputted as a time series signal.
There has been proposed a method in which exposure and reading are carried out repeatedly, multiple times in order to obtain a wide dynamic range in a solid state image-pickup device having such an arrangement as described above. In order to realize the method, a system is constructed as shown in FIG. 4. In the system, a switching means 102 is connected at its movable contact to an output terminal Q' of a solid state image-pickup device 101 (corresponding to the solid state image-pickup device in FIG. 3). One fixed contact a of the switching means 102 is connected to one input terminal of a signal processing circuit 104 through a memory 103, while the other fixed contact b of the switching means 102 is connected directly to the other input terminal of the signal processing circuit 104.
FIG. 5 is a flowchart showing the process of the case where the dynamic range is expanded through two exposure operations. In FIG. 5, first, a first time exposure is performed for a predetermined time T.sub.1 in the condition where the movable arm of the switching means 102 is connected to the contact a in a routine 100. Then, signal charges generated in the respective photodiodes are transferred to the vertical transfer lines in a routine 110; one row of the signal charges are transferred to the horizontal transfer line in a routine 120; and the one row of signal charges are outputted as a time series signal to the horizontal transfer line in a routine 130, so that the one row of signal charges, that is, the time series signal, is stored in the memory 103. Next, if it is determined in a routine 140 that all the signal charges have not yet been completely outputted, the operation is shifted to the routine 120 again. Thus, the operation is repeated until all the signal charges have been completely outputted.
Upon completion of the outputting of all the signal charges (at this point of time, all the signals by the first time exposure have been stored in the memory 103), the movable arm of the switching means 102 is switched to the fixed contact b, and the operation is shifted to a routine 150 so as to perform a second time exposure. Processing similar to that in the routines 110 through 140 is performed in succeeding routines 160 through 190. In the case of the second time exposure, the output signal is supplied directly to the signal processing circuit 104, and the first time signal, previously stored in the memory 103, is supplied to the signal processing circuit 104 at a predetermined time. Accordingly, a video signal Sv such as a color difference signal and so on are formed in the signal processing circuit 104.
Thus, an image is picked up through the employment of multiple processing operations which are different in exposure time from each other, so that a subject having high luminous intensity can be photographed without making the photodiodes saturate to thereby make it possible to substantially expand the dynamic range.
However, such a dynamic-range expanding method has disadvantages for the following reasons. First, since the respective exposure operations are performed through signal reading operations, the exposure timing for the respective exposure operations may largely shift so that a subject may move during the multiple exposure times. At any rate, even if a picture is reproduced on the basis of an obtained video signal, the subject in the reproduced picture may be displaced. Further, there is another problem in that it is necessary to separately provide such a memory for temporarily storing signals as shown in FIG. 4.